We are interested in learning the biological functions of repeated DNS sequences found in the eukaryotic genome. Our immediate plans are to further study the detailed arrangement of repeated sequences in the human genome and to test the relationship of these sequences to various transcription products. Regarding this latter study by standard renaturation studies, we wish to decide if the small nuclear RNAs (snRNAs) are copied from interspersed repeated sequences. We wish to test the possible relationship of approximately 300 NT. long interspersed repeats to clustered arrangements of 300 NT repeats, which have been recognized by restriction digestion patterns. We also plan to estimate the number of thoes interspersed repeated sequences which have the highest repetition frequency. This will be attempted by restriction endonuclease digestions of this sequence class. Single copy DNA sequences were (approximately 70%) previously found to be largely composed of distantly related repeated sequences of a very low repetition frequency. We plan to test if these duplicate sequences are genetically active by testing their ability to hybridize with m-RNA. This would be evidence for massive gene duplication in the human genome. This possibility would indicate that interspersed repeated sequences function at the level of RNA. We also plan to test if snRNA can hybridize with heterogeneous nuclear DNA, a messenger RNA precursor.